Carbon fibers are inorganic polymer fibers having a carbon content of more than 90%. The carbon fibers having a carbon content of more than 99% are referred to as graphite fibers. The micro-structures of carbon fibers are similar to those of artificial graphite and are turbostratic graphite structures. The spacing between carbon fiber layers is about 3.39 to 3.42A, carbon atoms between the parallel layers are not as regular as graphite, and the layers are connected by means of Van der Waals' force. The carbon fibers are a new material with excellent mechanical properties. The carbon fibers have a tensile strength of about 2 to 7 GPa and a tensile modulus of about 200 to 700 GPa. The density is about 1.5 to 2.0 grams per cubic centimeter, which is mainly determined by the temperature of carbonization in addition to the structures of the raw fibers. Generally, the density can reach 2.0 grams per cubic centimeter by graphitization at a high temperature of 3000° C. In addition, the carbon fiber is very light, its specific gravity is lighter than that of aluminum and less than ¼ of steel, and its specific strength is 20 times that of iron. The carbon fibers have a thermal expansion coefficient different from that of other fibers, and have the characteristic of anisotropy. The specific heat capacity of the carbon fibers is generally 7.12. The decrease in thermal conductivity with temperature rise is a negative value (0.72 to 0.90) parallel to the fiber direction and a positive value (32 to 22) perpendicular to the fiber direction. The specific resistance of carbon fibers is related to the type of the fibers. At 25° C., the high modulus is 775, and the high-strength carbon fibers are 1500 per centimeter. Thus, the carbon fibers have the highest specific strength and specific modulus among all high-performance fibers. Compared with titanium, steel, aluminum and other metal materials, the carbon fibers have the characteristics of high strength, high modulus, low density, small coefficient of linear expansion and the like on physical properties, and can be called the king of new materials. In addition to the characteristics of ordinary carbon materials, the carbon fibers have remarkable anisotropic softness, can be processed into various fabrics, and show high strength along the fiber axes due to their small specific gravity. Carbon fiber reinforced epoxy resin composite materials have the highest comprehensive indexes including specific strength and specific modulus among the existing structural materials.
After the carbon fiber material is formed by resin bonding, it has excellent properties such as high mechanical strength and low density, and is often used in bicycle bodies, automobile bodies, automobile hubs and other occasions. When it is used to manufacture a carbon fiber hub, the weight of the hub can be reduced by more than 30% compared with an aluminum alloy hub, so it has a broad prospect of weight reduction.
However, the surface of the carbon fiber reinforced resin-based composite product has many micropores, so that the surface protection treatment of the carbon fiber reinforced resin-based composite material become more difficult.